The present invention relates to a high speed tire testing device which is constructed with linkages to compensate for the elastic deformation of the structural components supporting the tire.
In the prior art, there are a number of tire testing machines of various kinds such as shown in U.S. Pat. Nos. 3,060,734, 3,206,973, 3,543,576, 3,546,936, 3,604,245 and 3,797,306. These devices typically include large frames that are required for moving the tire into position against a testing wheel. Such cumbersome mechanisms increase the cost of construction and make installation and servicing difficult. None of these devices provide an efficient, relatively lightweight and accurate tire testing apparatus that can be easily instrumented to provide for an analysis of all of the required loads and movements necessary for tire compliance testing.
Tire uniformity measurements are primarily associated with an assessment of the radial, fore/aft, and lateral force variations to be expected at the center of a tire rolling at a constant loaded radius, with aligning, overturning, and rolling resistance moments being of secondary importance. The need for tire uniformity measurements arose from the fact that the tire can be an exciter of vehicle vibrations. Previously, this sensitivity was mostly related to the first harmonic of the tire's non-uniformity. This first harmonic sensitivity feels very much like tire unbalance, having a once-per-tire revolution excitation rate.
The force variation signals from a tire can be decomposed into a series of sinusoidal components wherein the component having one cyclic variation per tire revolution being called the first harmonic, that with two complete cycles per tire revolution being called the second harmonic, etc. When one of these harmonics excites a resonant mode of vehicle vibration, a noticeable disturbance may be felt inside the vehicle. Since the first harmonic force typically has the large peak-to-peak amplitude, that harmonic is usually the most noticeable. However, the higher harmonics become noticeable in the form of beating together, i.e., interfering and reinforcing one another. Nevertheless, typical tire uniformity measurements in the prior art have only included the first harmonic peak-to-peak values for the radial and lateral force variation signals from the tire since it was believed that low speed measurement of these quantities provided the necessary correlation to ride comfort ratings.
With the ever-increasing use of radial tires, which have lower resonant frequencies than bias ply tires, it has become important to measure higher harmonic excitations because of the disturbances caused by these higher harmonics. A problem existed, however, because prior devices are not able to readily assess the disturbances produced by the higher harmonics. Moreover, the smaller and lighter vehicles being produced today with unibody construction are generally more sensitive to these higher harmonics, thereby producing an even greater need for such measurements.
Applicant's prior invention as embodied in U.S. Pat. No. 4,691,564, provides a high speed tire uniformity testing machine which is constructed such that no mechanical resonances exist within the measurement frequency range of approximately 1-200 Hz, thereby permitting the measurement of both higher harmonic excitation rates and increased fore/aft non-uniformity forces that increase with tire speed. Thus, the problem of prior devices not being able to readily assess the disturbances produced by the higher harmonics has been solved. However, another problem can arise with a relatively lightweight tire testing apparatus of this type. During the loading of a tire against a road wheel, the elastic deformation of the structural components supporting the tire may deflect to an extent that established machine alignment specifications cannot be met. Established specifications require parallel alignment between the tire and roadwheel shafts when loaded, and therefore, if either shaft deforms elastically during loading, such specifications cannot be met unless there is an appropriate compensation. Since the elastic deformation typically occurs in the tire shaft, there exists a need to compensate for that deformation.
Therefore, it is the object of the present invention to provide a high speed tire testing device which will compensate for the elastic deformation of the structural components that support the tire during the loading of the tire against a roadwheel.